390 w/open chamber heads

I should clarify, when i say CC the chambers. i am referring to the process of measuring the chambers for determining overall volume for the compression ratio.

you are correct, if you are going to cut the chambers to make them all equal you should do it before you get the new valve seats installed

Once they are all equal, they will stay equal no matter what valves are installed.

But changing from 1.88" to 2.02" intake valves will remove about 3.5cc from the chamber.

I don't know where you read that a 1.88" valve can be fitted to the exhaust of a mopar small block. But with factory cylinder heads that's definitely not possible.

unless you are building an all out race motor 2.02" and 1.6" is all you'll need. In fact, even race motors tend to keep the 1.6" exhaust valve and put a 2.08 in the intake.